(1) She already knows how a Patronus is cast, she just can’t do it yet.
(2) The text Harry gave Hermione is not actually teaching a spell. It is a cryptically-written secret about what Dementors are and what the charm does, not how to cast it. Knowing the secret will allow her to discover the new Patronus, not teach it to her.
Read it? Probably.
Understand it despite the Interdict of Merlin? Not so sure.
(1) She already knows how a Patronus is cast, she just can’t do it yet.
(2) The text Harry gave Hermione is not actually teaching a spell. It is a cryptically-written secret about what Dementors are and what the charm does, not how to cast it. Knowing the secret will allow her to discover the new Patronus, not teach it to her.